IncidenceIncidence: variable. It has been estimated that between 3.4 and 13.5 % of subjects in the USA are allergic to Thuya P. For certain types of tree, an IgE-dependent mechanism may be implicated e.g. in red cedar the allergen is plicatic acid (PA and TCPA). For the Samba, there are many major allergens, the predominant one being of 28 kDa (SDS, PAGE, IgE, BLOT). In the case of tropical woods a role for quinones has been implicated. Reactions with immunocomplexes can occur.Anti-parasitics used may also play a role on occasion e.g. pentachlorophenol and as well as moulds such as Neurospora (plywood)

ConditionsSensitization is directly linked to the size of the sawdust particles inhaled. Glues, varnishes, isocyanates and wood treatments may also play a role. In Canadian sawmills, the typical level for symptoms due to dust is 1.35 mg/m3. On the other hand, MDI (methylene-diisocyanate ) is used in the fabrication of laminates and workers exposed to this product (2 year study) can develop a large number of asthma-like symptoms (30%). In plywood factories and in woodcutting, the neurospora mould has been implicated in the development of asthma.

SymptomsAsthma may appear between 1 and10 years after initial exposure to the risk. It is often preceded or accompanied by rhinitis, conjunctivitis and urticaria (mukali). Attacks may be immediate or delayed and may continue for a long time after the subject has stopped working. The patient may develop concomitant eczema. Recent studies have demonstrated that the bronchial inflammation found in asthma caused by red cedar is identical in atopic and non-atopic subjects.

Diagnostics methodsSkin prick and intradermal tests. In the case of Thuya P: PA conjugated with HSA or TCPA-HSA; in the case of other woods test are performed with sawdust extract.

Immunological assays: ELISA, PTRIA with PA-HAS. In the case of Samba, a skin prick test can be performed with extracts in weight/volume.